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Bad Air Filter: Signs, Symptoms, and Replacement Cost

The engine air filter is a simple device that does a lot for your engine. It keeps dust and dirt out that would otherwise wear away at engine components, making them fail quicker than if your vehicle did not have any air filter at all.

If your engine air filter is bad, your vehicle could suffer from poor performance, suffer from poor fuel economy, produce black smoke from the exhaust, lead to a misfire, or create unusual engine noises.

What Is an Air Filter?

engine air filter

The engine air filter is often mistaken for the cabin air filter – the usually square, fanlike device the Jiffy Lube employees always show you and say needs to be replaced every time you get an oil change. The cabin air filter and engine air filter both do essentially the same thing, but the engine air filter is a line of defense against dirt, dust, and other objects that might otherwise get into and clog your engine. 

Its job is to filter out particles before they get passed through your engine, helping to feed clean air into the combustion chamber, thereby allowing your engine to run optimally. Though they vary in location depending on the vehicle, they are usually easy to locate by opening the hood, finding the airbox – if there is one – and popping it open. Your owner’s manual will have the exact location for the air filter in your specific vehicle. 

Common Signs and Symptoms of a Bad Air Filter

Since the engine air filter has so much to do with airflow into the engine and the cleanliness thereof, many of the signs and symptoms of a bad air filter are caused by dirty air affecting other systems of the vehicle or the decrease of airflow into the engine. 

A Visibly Dirty Air Filter

dirty air filter

The most common sign of a bad air filter is the visible dirt that accumulates on one. Most vehicles have an easily accessible filter that only requires removing the filter housing – or airbox. A clean filter is usually white or yellowish in color, and a dirty one looks much like the filter in a dirty vacuum cleaner would.

Your owner’s manual should have the size of your stock air filter so you know which one to order when it is time for a replacement.

Poor Engine Performance

Because dirt accretion can inhibit airflow into the engine, all areas of engine performance could suffer if the filter is dirty enough. Poor acceleration, engine hesitation, rough idling, and running roughly at speed can all stem from this. 

It usually takes a lot of dirt buildup and neglect to get to the point where your engine is visibly stressed simply as a result of a clogged air filter. More often, this happens over time, and engine performance slowly drops. This is why it is important to check your air filter periodically and replace it when necessary.

Poor Fuel Economy

A bad air filter can cause fuel economy issues, again, due to the restriction of airflow into the engine. This is because the engine has to work harder to get the air it needs when air is not easily attainable. It is also possible that dirty air or the lack of air to achieve the correct air-fuel ratio causes the engine to run poorly, also causing a decrease in fuel economy.

Black Exhaust Smoke

Exhaust is usually colorless. Blue exhaust smoke is usually a sign that your vehicle is burning oil, but black smoke can be a sign that your engine is burning up dirt and dust particles that have blown by or through the air filter. These particles can also cause the spark plugs to become fouled and burn excess fuel or oil.

Unusual Engine Noises

You know your vehicle better than anyone else, and when you hear an abnormal noise, it usually raises the alarm right away that something is wrong. Though not as common as some other signs and symptoms, unusual noises can come from your engine if the air filter is bad, mainly due to fouled spark plugs, misfiring, or other issues related to particles being sucked into the engine.

Engine Misfiring

Anytime the spark plugs in your engine get clogged with debris and oil, they will function at a decreased capacity or not at all. This causes misfires in the engine, also contributing to poor overall performance. The longer the air filter allows debris to pass by, the greater chance your spark plugs will fail and cause misfiring issues.

Engine Stalling or Failure

When misfiring becomes severe enough, it can cause engine stalling. Because misfiring is the lack of combustion with one or more combustion chambers, the extent of the misfiring will have a comparable effect on the performance of your engine. Additionally, consistent misfiring can cause damage to the internal components of the engine.

Check Engine Light Illumination

The check engine light is the “catch-all” symptom of a host of different root issues. This can include various problems caused by a bad air filter. The light will not illuminate if your filter is too dirty, but any one of the issues above, including fouled spark plugs, engine misfiring, and fuel economy issues can all trigger the check engine light.

Many automotive retail locations offer free OBD scans to read check engine light error codes. Normally, other symptoms consistent with a bad air filter will also be present if or when the check engine light illuminates and the root cause is a bad air filter.

What is the Expected Lifetime of an Air Filter?

checking air filter

Each vehicle is a little different and manufacturers have various recommended change intervals, but most mechanics and manufacturers recommend changing your engine air filter every 15,000 to 30,000 miles. Your owner’s manual will have recommended change intervals for your specific make and model. Regardless, you should always change your air filter when it gets dirty. 

There are not too many things that cause air filters to fail unexpectedly since they are simple devices that have no active movement, no mechanical or electronic components, and are usually protected by an airbox. However, large objects, excessive dirt, and water all have the potential to damage an air filter prematurely under the correct circumstances. 

How Much Does an Air Filter Cost to Replace?

Fortunately, because air filters are so simple, they do not cost nearly as much as other engine parts. Additionally, they are usually easy to replace since they are one of the more accessible components under the hood. This means that you can often save labor costs and replace the air filter yourself if you know where it is. 

Air filters themselves usually cost between $30 and $60, depending on the size and model of your vehicle. If you choose to have a mechanic install your new air filter, labor costs can range from $25 to $35. In total, air filter costs are usually well under $100, especially if you choose to do it yourself. Costs for the most expensive air filters in the hardest-to-reach locations can touch or exceed $100.

Final Thoughts

Air filters are simple components that play a vital role in ensuring that clean air can be used by your engine to help it run optimally. A dirty air filter will exhibit several symptoms, including decreased engine performance, decreased fuel economy, misfiring, black exhaust smoke, and even the illumination of the check engine light. Fortunately, air filters are both inexpensive and easy to replace should any of these signs and symptoms exhibit themselves.

Shawn Furman
I have been a vehicle hobbyist for as long as I can remember as well as a freelance writer for the past three and a half years. My clients have included Vehicle Scene, Autolist, CarGurus, and now The Vehicle Lab. In addition to my current clients, I also maintain my own blog where I am able to share my knowledge and experience through vehicle reviews, car-buying guides, how-to guides, and list articles.
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